In this column we will look at tick bites, focusing on Rocky Mountain spotted fever and Lyme disease. These are diseases that are transmitted to humans when they are bitten by an infected tick. Ticks go through a complicated life cycle beginning as an immature larval stage progressing to an adult phase. They depend on blood meals to move through each stage. If a tick ingests a microorganism at any one of it's blood meals it can pass it on to it's next host. This is where we come in. Hunters are at high risk because we spend a lot of time in the woods. When the tick bites you it can transmit microorganisms into your system. These microorganisms are the cause of our troubles. This is important to understand. Not all tick bites cause disease because not all ticks are infected. This has led to some controversy as to which tick bites should be treated with antibiotics. It really depends on what part of the country you were bitten in and what percentage of ticks are infected. So, a tick bite in Vermont carries a lesser risk than a bite in Pennsylvania and should be treated as such. We will now look at the two most prevalent tick borne illnesses and how to treat them.
Rocky Mountain Spotted Fever
I bet you thought that Rocky Mountain spotted fever describes how you feel when a big bull sees you at 8 yards as you come to full draw. You would think that with a name like Rocky Mountain spotted fever this would be a disease that only western elk hunters would have to worry about but unfortunately this is not true. The disease is seen throughout most of the US and is very common in areas of the southeast such as Virginia and North Carolina. The midwest is not spared and Oklahoma and Kansas also have high rates of disease. The microorganism that causes Rocky Mountain Spotted fever is named Rickettsia rickettsii. The tick carrier varies depending on what part of the country you live in. In the west the wood tick is the carrier and in the southeast the dog tick is the major culprit.
Rocky Mountain spotted fever produces a serious infection which typically presents 5 -7 days after the tick bite. Fever, swelling and rash are the symptoms which should suggest Rocky Mountain spotted fever. The rash starts on the wrists, palms, ankles or soles of the feet. Unfortunately the rash is not always present in the early stages of the disease. The fever can be quite high reaching 103 to 104F. The swelling (medically called edema) is due to damaged leaky blood vessels from the infection and occurs throughout your body.
Other symptoms include severe headache, lethargy, and joint pains. Unfortunately, there are no good early tests to diagnose Rocky Mountain spotted fever. The blood test doesn't become positive until you have had the disease for 2-3 weeks which is too late for early treatment. The symptoms are not specific to this disease and without a history of a tick bite the early diagnosis can be difficult. You hog hunters in the southeast need to tell your physicians that you have been out playing in the woods and could have been bitten by a tick!
The treatment for Rocky Mountain spotted fever is doxycycline or tetracycline. The earlier the antibiotic is started the better the chance for full recovery. At this time, prophylactic treatment after tick bite or removal is not recommended because this changes how the disease presents and could make the microorganisms resistant to antibiotics. If you remove a tick or note a tick bite and develop a fever, rash or the other symptoms we talked about, then you should let your physician know about the bite and then be treated with antibiotics.
Lyme disease is transmitted by Deer ticks and initially was identified around Lyme Connecticut. The microorganism which causes Lyme disease is Borrelai burgdorferi. In the early 1980's the cases were mainly clustered in the Northeast but now Lyme disease has been reported in 43 states. The incidence varies widely from state to state and even within different counties. Most studies on tick bites indicate that the tick requires 24-48 hours of attachment to transmit the infection. This is probably true in the vast majority of cases although disease transmission has been documented with as little as 6 hours of attachment. In areas with a high incidence of infected ticks only 1-3 % of people with a known tick bite develop Lyme disease. The risk of disease clearly increases with the duration of attachment. Unfortunately, many people who develop Lyme disease don't remember a tick bite.
Once you are infected, Lyme disease is divided into 3 stages. The initial stage is a rash called Erythema migrans which typically appears 7-10 days after the tick bite. The rash looks like a bullseye and occurs at or near the site of the bite. About half the people who develop the rash will also have a flu like illness with fever, joint pains and a headache. Untreated, the rash will disappear in about 2 weeks but you still carry the infection. The second stage of the disease develops 4-6 weeks after the tick bite and is characterized by involvement of your heart and brain. Between 5-10% of infected people will have cardiac symptoms including irregular heartbeats or infection within the heart muscle. Luckily, heart involvement is self limited and usually resolves spontaneously. Nervous system involvement can develop in up to 40% of untreated individuals. Infection can involve both the brain(meningitis) and the peripheral nervous system (nerves coming off your spinal cord). Symptoms can include a severe headache, stiff neck, fever, facial droop or pain and numbness in an extremity. These symptoms also will resolve after 5-6 months if untreated, but improve more quickly with antibiotics. Arthritis marks the final stage of the disease. The knee is the most commonly involved joint although others are possible. The episodes of arthritis will last about a week but recurrences are common. About 10% of people will have long term arthritis. Many people at this stage also describe a constant feeling of fatigue and short term memory loss.
Treatment of Lyme disease is somewhat controversial. As with most medical problems we will discuss, prevention is much better than treatment. Permethrin treated clothing and DEET can help prevent bites. Since duration of the bite increases the risk of transmission, daily inspection and tick removal can go a long way toward decreasing the risk of disease. When removing the tick it should be grasped as close to the skin as possible with tweezers and removed with slow steady traction. The tick's body should not be squeezed as it might inject infectious material into your skin. Similarly, methods such as gasoline, kerosene, or a lighted match are not recommended. These methods typically will cause the tick to regurgitate infectious material into your skin as it dies. Treatment of an asymptotic tick bite depends on where you live and the duration of exposure. If you have the tick, bring it to your physician as only deer ticks carry Lyme disease. In most areas of the country, prophylactic treatment is not recommended. This decision can be discussed with your doctor. If you develop the characteristic rash, treatment is successful with a wide variety of agents including amoxicillin and doxycycline. For the more advanced stages of the disease a blood test can help make the diagnosis. This test is often negative in the early stages of the disease but should be positive by the time symptoms beyond the rash develop. Treatment at these stages involves more potent antibiotics at higher dosages and for longer courses. Luckily most cases are responsive to antibiotics and good recovery is the rule. For more information on tick borne diseases the American Lyme Disease Foundation has an excellent website at www.aldf.com
*Pictures courtesy of the American Lyme Disease Foundation
Next month: Snake bites